1. Field of Invention
The present invention relates to a high-brightness color liquid crystal display (LCD) panel employing non-absorptive spectral filtering and light recycling among neighboring subpixels, and also to methods and apparatus for manufacturing the same.
2. Brief Description of the Prior Art
Without question, there is a great need for flat display panels capable of displaying video imagery in both direct and projection modes of viewing. Examples of equipment requiring such display structures for direct viewing include notebook computers, laptop computers, and palmtop computers, and equipment requiring such display structures for projection viewing include LCD projection panels and LCD image projectors.
In general, prior art color LCD display panels have essentially the same basic construction in that each comprises the following basic components, namely: a backlighting structure for producing a plane of uniform intensity backlighting; an electrically-addressable array of spatial-intensity modulating elements for modulating the spatial intensity of the plane of backlight transmitted therethrough; and an array of color filtering elements in registration with the array of spatial-intensity modulating elements, for spectral filtering the intensity modulated light rays transmitted therethrough, to form a color image for either direct or projection viewing. Examples of such prior art LCD panel systems are described in "A Systems Approach to Color Filters for Flat-Panel Displays" by J. Hunninghake, et al, published in SID 94 DIGEST (pages 407-410).
In color LCD panel design, the goal is to maximize the percentage of light transmitted from the backlighting structure through the color filtering array. However, using prior art design techniques, it has been impossible to achieve this design goal due to significant losses in light transmission caused by the following factors, namely: absorption of light energy due to absorption-type polarizers used in the LCD panels; absorption of light reflected off thin-film transistors (TFTs) and wiring of the pixelated spatial intensity modulation arrays used in the LCD panels; absorption of light by pigments used in the spectral filters of the LCD panels; absorption of light energy by the black-matrix used to spatially separate the subpixel filters in the LCD panel in order to enhance image contrast; and Fresnel losses due to the mismatching of refractive indices between layers within the LCD panels. As a result of such design factors, the light transmission efficiency of prior art color LCD panels is typically no more than 5%. Consequently, up to 95% of the light produced by the backlighting structure is converted into heat across the LCD panel. Thus, it is impossible to produce high brightness images from prior art color LCD panels used in either direct or projection display systems without using ultra-high intensity backlighting sources which require high power supplies, and produce great amounts of heat necessitating cooling measures and the like.
In response to the drawbacks of prior art color LCD panel design, several alternative approaches have been proposed in order to improve the light transmission efficiency of the panel and thus the brightness of images produced therefrom. For example, U.S. Pat. No. 5,325,218 to Willett et al. discloses an LCD panel which uses tuned cholesteric liquid crystal (CLC) polarizers to replace absorptive dyed (neutral or dichroic) polarizers of prior art LCD panels to improve color purity, and a partial (i.e. local) light recycling scheme in order to improve the brightness of the LCD panel. U.S. Pat. No. 5,418,631 to Tedesco also discloses an LCD panel which uses a holographic diffuser for directing light out from the light guiding panel of the backlighting paneling structure, and CLC polarizers for locally recycling light diffused by the holographic diffuser in order to improve the brightness of the LCD panel. However, such prior art color LCD panel designs are not without shortcomings and drawbacks.
In particular, notwithstanding the use of non-absorptive CLC filters and localized light recycling principles, prior art LCD panels continue to require at least one light absorptive layer along the optical path extending from the backlighting structure to the viewer (i.e. along the light projection axis). Consequently, prior art LCD panels have very low light transmission efficiencies. Thus the production of high brightness color images from prior art LCD panels has required high-intensity backlighting sources which consume great amounts of electrical power and produce high quantities of heat, and necessitate the use of fans and other cooling measures to maintain the temperature of both the LCD panel and the lamp(s) in the backlight structure within safe operating limits.s
Thus, there is a great need in the art for an improved color LCD panel which is capable of producing high brightness color images without the shortcomings and drawbacks of the prior art LCD panel devices.